Device for making current measurements used in determining the charging of a vehicle storage battery

ABSTRACT

A device for making current measurements used in determining the charging status of a vehicle storage battery, comprising a ground conductor connected between one pole of the storage battery and the ground contact. The pole is connected via electrical conductors to a sensor having a source of electric power for providing at least one electric current to the ground connector. Values which are deducted from the current flowing through the ground conductor are provided to a microprocessor to determine the charging status of the battery.

FIELD OF THE INVENTION

The present invention relates to a device for determining the chargingstatus of a vehicle storage battery, comprising a ground connectorconnected between one pole of the storage battery and a ground contact,and which is further connected to sensor means for sensing the flow ofcurrent.

BACKGROUND OF THE INVENTION

There is a demand for the ability to monitor the charging status in thestorage battery of a vehicle. After a number of cold starts, trips withsmall mileage or with use of energy demanding extra equipment in thevehicle, there is a risk that the effective output of the generator willno longer be sufficient to drive all equipment and simultaneously giveenough energy for recharging the storage battery. Furthermore, anaccumulator battery is successively aged, which means that over time ittakes a longer time to recharge it and the total accumulator capacity isreduced. Power dissipation may also occur in the generator or otherparts of the electrical system so that the output of the generator isreduced or a voltage drop occurs.

Having access to information about the charging status of the battery,the driver of the vehicle can be in a better position to avoid startingproblems, e.g. by changing an old battery, by adjustment of the powerconsumption so that the battery receives proper charging or byadditional recharging of a temporarily run-down battery.

Known means for determining the charging of a battery does not considerthe age of the battery, and typically use rather deliberate andexpensive sensor means for detection.

SUMMARY OF THE INVENTION

One object of the present invention is therefore to provide a simple andefficient sensor which can be used for determining the charging statusof a storage battery.

This object is achieved according to the invention in that the sensormeans comprises a source of electric power for providing at least oneelectric current through a ground connector, at least one currentmeasuring unit, and means for processing electrical signals, whereinvalues which are deducted from the current flowing through the groundconnector are provided to the processing means and are used fordetermining the charging status of the storage battery.

According to a preferred embodiment of the present invention, the groundconnector is connected to the battery pole and body or the chassis ofthe vehicle, and the ground connector and the electrical conductorswhich connect the ground connector to the sensor means may form a commoncabling. Thus, the sensor will be simple to integrate in the wiringsystem of a vehicle.

Preferably, the cabling comprises an uninsulated cabling ground braidwith a cable shoe or connector in each of its ends and two insulatedconductors, one end of which is connected to the respective cableconnector and wherein the other ends are connected to the sensor means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the basic construction of the device for determining thecharging status of a storage battery diagrammatically showing thestorage battery connected to a vehicle according to the invention.

FIG. 2 is a block circuit diagram showing the measurement system inwhich the present invention is used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, reference 10 generally designates a storagebattery conventionally connected with both its poles 11 and 12 to thewiring system of a vehicle via a ground connector 13 and a currentconnector 14. Each end of the ground connector 13 is provided with acable connector 15 and 16 respectively and is mounted with a metallicconnection by screws to the vehicle body 17 and cable connector 16 sothat it can be used as a return conductor to the battery by thegenerator 33 and the power consumers in the wiring system, e.g., outerand inner lighting, air-conditioning, radio and so on.

The storage battery 10 is used conventionally, to deliver energy to astarter motor for starting a combustion engine and to provide a storagemeans for the energy consumption when the output of the generator aloneis not sufficient for balancing the energy consumption in the electricalsystem of the vehicle. The battery 10 is recharged for as long as thevoltage is lower in the battery than in the electrical system.

The battery status, i.e. the amount of charge, depends upon severaldifferent parameters, such as the discharging current and the poletension, temperature, capacity and age of the battery. Information ofthese parameters can, according to the present invention, be obtained bymeans of a sensor or measuring shunt comprising ground connector 13which is mounted between body 17 and the battery pole 11. Groundconnector 13 can, without any special efforts, be devised in such waythat it presents a suitable resistance, for example 1 mΩ. Thisresistance can be utilized for measuring the battery current and thetension over the two shunt points 15 and 16.

For this purpose, insulated electrical conductors 18 and 19 have beenconnected to each of the cable connectors 15 and 16. Electricalconductors 18 and 19 connect both cable connectors to 15 and 16 to acentral unit 20, preferably comprising a micro processor 40, currentmeasuring units 22 and 23, a source of constant current 25 forproduction of at least one current, and an interface unit 24 foradapting the input signals from battery temperature sensor 31 and enginespeed sensor 32.

The resistance in ground connector 13 depends, for example, uponoxidation on the metallic connections of shunt points 15 and 16, body 17and battery pole 11. Therefore, central unit 20 must be updated withincertain intervals regarding this parameter, as well as in regard toother parameters concerning battery and engine temperature. To this end,current source 25 is used and voltage across ground connector 13 ismeasured to determine the resistance in ground connector 13 during ameasuring sequence. The charging status of battery 10 is determined byknown methods such as the method disclosed in Swedish Patent No.9001137-0. In this regard, the system is either in a state of rest or inan active state. When the system is in its active state, the batterycurrent flowing through the ground connector is measured during acertain time period. From these measurements, a value of the availablequantity of charge is derived by "counting" the amperehours into and outof the battery respectively. This value is compared with the quantity ofcharge of a fully charged battery, giving a value of the charging statusq of the battery. The value of q is represented as a percentage, ascompared to a fully charged battery. There is also compensation for aconversion efficiency in connection with the charging and discharging ofthe battery at different values of the temperature and charging statusof the battery. The value of the charging status q may be utilized forshutting down a certain electrical load when the charging status is low,for example, or for indicating to the driver that the charging status islow.

A presentation unit (not shown) is connected to central unit 20 via awiring 21 and is placed at the instrument panel of the vehicle, so thatthe charging status of battery 10 can be displayed to the driver. Thepresentation unit can comprise any type of conventional display meanslike a pointer, a warning light or similar types of indicatorinstruments within the field.

The sensor according to the invention can be applied together with thecentral unit and presentation unit to various types of vehicles, forexample passenger cars and lorries, motorcycles and leisure boats.

The invention is not limited to the above described embodiment exampleand more variations are possible within the scope of the followingclaims. For example, the connector 13 may compose an uninsulated braidedground cable or alternatively some form of insulated conductor.Furthermore, any kind of conductor which connects the car body and thebattery pole can be used.

We claim:
 1. A device for making current measurements used indetermining a charging status of a storage battery of a vehicle having apair of poles, comprising a ground connector electrically connectedbetween one of the pair of poles and a chassis of the vehicle via aground contact, sensor means for sensing a flow of current, and firstand second electrical conductors electrically connecting said groundconnector to said sensor means to form a common cabling, said sensormeans comprising a source of electrical power for providing an electriccurrent through said ground connector, at least one measuring unit formeasuring said current flowing through said ground connector, andprocessing means for processing electrical signals, wherein values whichare deduced from said current flowing through said ground connectorrevealed by said measuring unit are provided to said processing meansfor use in determining the charging status of the storage battery.
 2. Adevice as claimed in claim 1, wherein said common cabling comprises anuninsulated ground braid having a cable connector at each end of saidbraid, and one end of each of said first and second electricalconductors being connected respectively to each said cable connector andthe other end of each of said first and second electrical conductorsbeing connected to said sensor means.